1. Field of the Invention
The present invention relates to a method for testing a thin film structure, particularly to a method for testing a state of a thin film structure by detecting a structural defect, such as a pinhole, in the formed thin film by utilizing scattered light which is caused by the defect when light flux is projected to the defect.
2. Related Background Art
Recently, the ordered structure of organic materials (or organic molecules) has come to be noticed in connection with development and improvement in electronic functions. In particular, electronic devices employing organic molecules are attracting attention.
As for the techniques of constructing molecular electronic devices, many reports have been disclosed regarding Langmuir-Blodgett films (LB films).
An LB film is constituted of a regular lamination of monomolecular layers of an organic compound. The LB film has enabled formation of a uniform ultra-thin film by controlling the film thickness thereof in the order of the unit of a molecular length. Many attempts have been made to use the LB film as an insulator.
Examples of the attempts include a tunnel junction element having a structure of metal/insulator/metal (MIM) [G. L. Larkins, et al.: "Thin Solid Films", Vol. 99 (1983)]; a light-emitting element having a structure of metal/insulator/semiconductor (MIS) [G. C. Roberts, et al.: Electronics Letters, Vol. 20, p. 489 (1984)]; and a switching element [N. J. Thomas, et al.: Electronics Letters, Vol. 20, p. 838 (1984)].
Even after the investigations of characteristics of the elements in these studies, the problems still remain unsolved such as variation of the properties of respective elements and deterioration by aging thereof which are considered to be ascribable to structural defects in LB films, causing lack of reproducibility and of stability.
One of the problems in detection of a structural defect of an LB film, is that the structural defect of the LB film is required to be visualized and to be numerically evaluated within a limited time.
In conventional evaluation, the results are shown as indirect and average data such as in a copper metallizing process [I. R. Peterson: Aust. J. Chem., Vol. 33, p. 173 (1980)]; and measurement of electroconductivity for an MIM structure [P. Lesieur, et al.: Thin Solid Films, Vol. 152, p. 155 (1987), and I. R. Peterson: J. Mol. Electron., Vol. 2, p. 95 (1986)].
Further, the evaluation by electron microscopy is complicated for the evaluation of structural defects of an LB film because many parameters have to be controlled to obtain significant results. Therefore, the electron microscopy requires technical skill as well as much time for the measurement.